Polymeric fibres, films, coatings and moulded products are ubiquitous in modern society, and are used in applications as diverse as packaging materials, clothing, medical devices, etc. Mechanistic and kinetic considerations are useful in the development of efficient catalysts for controlled selective polymerisations, which is essential for the production of polymeric materials possessing properties tailored to suit their application. Mercury-based compounds are used as catalysts in many applications of the synthesis of polyurethanes such as the production of polyurethane elastomers. Due to the environmental impact of mercury, there is a need to replace such catalysts with complexes based on benign metals. Group 4 metals are an attractive option, both in terms of reactivity and their benign environmental nature. A series of novel complexes have been synthesised, fully characterised, and their activity and selectivity investigated in a model reaction. The molecular structures of a number of potential catalysts have been determined by single crystal X-ray diffraction experiments. These potential catalysts have been screened in the model reaction utilising in situ reaction monitoring in order to acquire kinetic data. A method to study catalyst selectivity has also been developed. The results of these kinetic and selectivity studies are presented in this thesis and compared to the industrial phenylmercury neodecanoate catalyst system. A selection of well-defined complexes which have been synthesised as part of this body of work have also been evaluated in the preparation of polyurethane elastomers. Physical characterisation techniques such as Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and Scanning Electron Microscopy (SEM) have been used for this purpose.